Induced draft gas furnaces are commonly used to generate heat for residential and commercial use. Such furnaces vary in design, but at their core serve the basic function of igniting gas (typically natural gas or propane) and air, and directing the resulting combustion gases to a heat exchanger. The combustion gases are of an elevated temperature and by directing same through serpentine conduits provided as part of the heat exchanger, air to be heated can then be directed across the heat exchanger to extract heat from the heat exchanger. A blower motor provided as part of the furnace can be used to create the air flow across the outside surface of the heat exchanger. The heated air then exits the furnace and by way of ductwork is communicated to the rooms or space needing to be heated.
The heat exchangers of such furnaces typically employ a plurality of heat exchanger coils, each one having a burner associated with an inlet to the coil. The burner serves the function of mixing the gas and air and igniting same to generate a flame. The burner outlet with such prior art designs is positioned close to, but spaced from, the heat exchanger coil so as to direct at least a portion of the flame into the heat exchanger coil. The gas is typically introduced into the burner by way of a gas supply controlled by a processor of the furnace. The air needed for combustion is typically provided by way of another blower motor which pulls (induced draft) air through the burner and pulls the flame and combustion gases through the heat exchanger.
While effective and commercially successful, air quality regulations are becoming increasing stringent. For example, federal, state and local authorities regulate acceptable emissions standards of nitrous oxide (NOx), among others. The SCAQMD (South Coast Air Quality Management District) of California is one example of a regulatory body dictating a maximum emission rate of NOx. Given the current climate and popular opinion regarding the environment, these standards are likely to only get more restrictive in the future.
As a result of such regulations, prior art burners have had to be redesigned. Certain prior art burners, known as “in-shot” burners, included two sources of air: a primary source providing air to the inlet of the burner for mixing with the gas, and a secondary source at the outlet of the burner and prior to introduction of the flame to the heat exchanger. However, in order to reduce NOx emissions, that secondary source of air has to be eliminated. While reduction in NOx emissions have been achieved in forced drafted system (blower at inlet) burners for use with induced draft furnaces which satisfy the emissions standards have not been introduced.